A conventional sliding bearing for supporting a crankshaft journal portion has been used as a cylindrical body formed by combining two semi-cylindrical bearings. In the sliding bearing, a circumferential oil groove is formed on an inner circumferential surface of at least one of the pair of semi-cylindrical bearings, through which circumferential oil groove oil is fed to an outer circumferential surface of a crankpin. In general, the circumferential oil groove has been made to have a constant depth (see JP-A-08-277831).
On the other hand, recently there has been made a proposal to form a narrow part where a sectional area of the oil groove is reduced from a bearing circumferential center part toward a bearing circumferential end part in order to decrease leakage of lubricant oil from the bearing circumferential end part in order to cope with a trend of size reduction of an oil pump for feeding lubricant oil (see JP-A-04-219521 and JP-A-2005-69283).